1. Field of the Invention
The fields of art to which this invention pertains are crystalline aluminosilicate adsorbent production and aromatic hydrocarbon isomer separation. More specifically, this application relates to a process for separating the para-isomer from a feed mixture comprising at least two bi-alkyl substituted monocyclic aromatic isomers, including the para-isomer, said isomers having from 8 to about 18 carbon atoms per molecule which process employs a particular crystalline aluminosilicate adsorbent.
2. Description of the Prior Art
There are numerous methods for the manufacture and ionexchange of various crystalline aluminosilicates, particularly the type X and type Y crystalline aluminosilicates, to yield products useful for effecting given hydrocarbon reactions or separations. My invention embodies both a manufacturing method for producing an adsorbent material having superior properties for aromatic hydrocarbon isomer separation and a process for the separation of the para-isomer from a feed mixture comprising at least two bi-alkyl substituted monocyclic aromatic isomers, including the para-isomer, the isomers having from 8 to 18 carbon atoms per molecule which process employes the particular adsorbent.
A common problem encountered with most adsorbents and many catalysts is dust which can form excessive pressure drop after the adsorbent or catalyst has been loaded into the adsorbent chambers or reaction vessel and has been used in the particular process. Certainly it is for the reason that adsorbents and catalysts are manufactured to meet certain minimum physical strength requirements and that they are loaded into chambers and vessels with care to avoid breakage. Although operations such as screening can be used to remove most of the interstitial smaller particles and dust, such operations generally fail to remove dust which may coat particles of adsorbent or catalyst of the proper size. This type of dust, apparently held to the particle by electrostatic attraction, may then later be removed by liquid passing through the adsorbent chamber or catalyst vessel and accumulate to form excessive pressure drops.
I have discovered that the troublesome dustiness characteristic of adsorbents is virtually eliminated by a fluoride treatment of the base material. It is thought that the fluoride solublizes the dust by reacting with combined aluminum compounds present in the dust thereby removing the dust from the particles.
I have, additionally, found that an ion-exchange of a base material with a fluoride-containing aqueous solution of sodium hydroxide followed by an ion-exchange with potassium and barium or with barium alone and then a drying step produces an adsorbent with faster transfer rates and higher aromatic capacity than adsorbents produced by either fluoride or caustic treatment alone or with untreated base. Although it is hypothesized that the ion-exchange with aqueous sodium hydroxide replaces non-sodium cations such as H+ or Group II-A cations occupying exchangeable sites within the zeolite and thereby permits higher amounts of barium and potassium or barium alone to be added during a subsequent ion-exchange step, the synergistic result obtained by combining the fluoride treatment with the sodium ion-exchange is neither expected nor understood.
The prior art has neither disclosed nor suggested the method of making this particular adsorbent nor the aromatic hydrocarbon isomer separation process employing the adsorbent.